Process for making polyurethane foam

ABSTRACT

A flexible polyurethane foam article with regions of different hardness is made by introducing into a mould a foam formulation giving a foam of a given hardness and then introducing a foam formulation giving a foam of different hardness directly onto the first foam formulation at a time corresponding to a volume expansion in the range 100% to 2300%.

The present invention relates to the production of foams which containintegrated foam areas having higher or lower hardnesses. Such foams areparticularly useful for seats.

Seats, especially car seats have to support the seated person understatic and dynamic conditions in a way that the supporting force iscompatibly distributed on to the human body. This means, that the mainforce is taken by the bones without squeezing the veins in the softerareas. In addition to this a seat needs to provide sufficient sidestability in case of side acceleration which exists when driving the carin curves.

It is therefore desirable for seats in particular for use in transport,e.g. car seats, to have relatively hard and relatively soft portions.Those skilled in the art of seat construction are familiar with theparts of the seat where it is desired to provide relatively hardportions.

It is well-known that seats may be made from polyurethane foams.Reinforced regions in such polyurethane foams are at present provided ina number of ways. One method is to prepare a foam part of increasedhardness and to introduce this separately prepared part into the softerfoam part. Another method is to embed steel wire frame inserts into theseat. A third method is for the supporting seat frame, to which thepolyurethane foam is attached, to provide additional support in therequired areas.

In addition to the above commercially use methods, polyurethane foamseats have been produced on an experimental basis by two methods. In onemethod a first moulding step is carried out to produce a layer of softfoam between two mould parts.

One of the mould parts is then removed and replaced by another mouldpart which defines a cavity containing the soft foam layer. A mixturegiving a harder polyurethane foam is then injected into the cavity.

Another method which had been tried experimentally is to use twoseparate machines for producing polyurethane foam which feedsimultaneously into the mould. It is then necessary to have a moulddesign or separating walls which keeps the two different foam mixturessubstantially apart but which allows sufficient contact between the twofoams to ensure good bonding on curing.

Any kind of insert which needs to be put into the moulds during foamseat production requires processing time, adds material cost andincreases repair and scrap rates.

Structural modification of the seat frame is limited and again addsproduction cost.

The new experimental processes described above require complicated andmore costly moulds (two lids) and need double processing time or areeither investment intensive or limited in hardness variation.

Furthermore it is required to have some kind of separating walls in themould which keep the liquid material for a short time in place.

The production of foam articles of different hardness without deviceswithin the mould to separate the harder and softer foams is disclosed inCanadian Patent Specification and German Patent Specification. In theprocesses described above in these two specifications formulationsgiving harder and softer foams are poured simultaneously into the mould.The Canadian specification on page emphasises the importance ofproviding grooves and depressions in the mould so that the differentfoam formulations are kept separate initially even though they aresubsequently allowed to come into contact with each other. In themoulding process specifically described in the German patentspecification a mixture producing harder foam is introduced into arecess in a mould corresponding to the side portions of the seat while amixture producing softer foam is fed into the centre of the mould. Thenew foam formulations are again kept apart initially. The requirementfor the foam formulations to be fed into the moulds in which they areinitially separated imposes restrictions on the types of mould which canbe used.

Furthermore, it is only possible to produce articles in which theregions of harder and softer foam extend to the surface of the article.It would be desirable to be able to produce articles of harder andsofter foams in which one type of foam extended over a substantial partof the other type of foam. For example, this would make possibleproduction of seats in which the surface layer had a desirable soft feelbut regions of harder foam were embedded within the car seat. The carseats disclosed in Canadian Pat. No. 789958 and German patentspecification No. 2523527, in which upwardly projecting side portionsconsisting only of harder foam are joined to a central portion of softerfoam have the disadvantage that when a person sits on the centralportion and depresses it there is a tendency for the harder foamportions to be deflected inwards towards the centre of the seat, whichis undesirable. This tendency for the side portions to be deflectedinwards can be reduced if a region of harder foam embedded in the softerfoam extends into the central portion between the upwardly projectingside portions. Until now there has been no simple way of making such carseats.

According to the present invention the process for the production of aflexible polyurethane foam article having regions of differing hardnesscomprises introducing into a mould first and second foam fomulationsgiving foams of different hardness prepared by mixing together a polyolstream and an isocyanate stream in a mixer characterised in that thesecond foam formulation in introduced directly on to the firstformulation at a time corresponding to a volume expansion of the firstfoam formulation in the range +100% to 2300%.

The term "foam formulation" means, as is well-known to those skilled inthis technology, the total mixture of ingredients required to give aflexible polyurethane foam.

The volume expansion of the foam formulation can be observed by feedingthe foam formulation into a container and measuring the height of thefoam at different times so enabling the time required for a given volumeexpansion to be determined.

The foam ingredients are usually fed into the mould through one or morenozzles which are moved across the mould so that the foam formulationwill be introduced into different parts of the mould at different timesalthough the time interval between the beginning and end of theintroduction of the foam formulation is preferably kept as short aspossible. The time of first introduction of the second foam formulationis such as to correspond to a foam expansion in the first foamformulation at the point at which the second formulation is introducedof at least +100%. Preferably any subsequent addition of the secondformulation is made at a time corresponding to at least 100% foamexpansion of the first foam formulation at the point at which the secondfoam formulation is added.

Various techniques have been disclosed previously for producingpolyurethane foam formulations of different hardness for making articlessuch as car seats. In Canadian Pat. No. 789958 the increased hardness inthe side portions is provided by adding a dense filler to theformulation intended to give the harder polyurethane. This however isnot a very satisfactory technique.

It is possible to vary the hardness of a polyurethane foam by varyingthe ratio of isocyanate index which is a well-known measure of therelative amounts of isocyanate polyol used to make it. The variation inhardness which can be obtained by this method is limited however.

It is possible to vary the amount of water used in the foam formulationso as to give a less fully expanded foam of higher density whichtherefore feels harder. However in the production of foam articleshaving regions of harder and softer foam it is preferred that theregions of increased hardness are composed of foams which are inherentlyharder than the softer foams rather than foams which are only harder byreason of having a higher density.

The different foam formulations can be prepared in various differentways. The final stage in the production of polyurethane foams is themixing together of a polyol, usually a polyether polyol, and anisocyanate. This is done in a mixing device which then discharges themixture into the place where it is to be foamed.

It is particularly preferred to carry out the process of the presentinvention using a foam formulations in which the formulations givingsofter and harder foams differ in their content of any one or more of:

1. isocyanate with a functionality greater than two, i.e. with more thatwo isocyanate groups per molecule, e.g. polyphenylmethylenepolyisocyanate

2. active hydrogen containing compound which may be

(a) chain extender

(b) cross-linker.

An increase in the proportion of isocyanate with a functionality greaterthan two i.e. with more than two isocyanate groups per molecule, e.g.polyphenyl methylene polyisocyanate and/or cross-linker will cause to anincrease in hardness.

An increase in the proportion of chain extender will cause a decrease inhardness.

The formulations of different hardness may be made using a mixturecontaining polyol which has been prepared in bulk in advance so as tocontain differing amounts of cross-linker or chain extender. Similarlyan isocyanate feed can be used which have been prepared in bulk inadvance so as to contain differing amounts of polyphenyl methylenepolyisocyanate.

However it is more convenient for the manufacture of polyurethane foamsto use a single main polyol feedstock and a single main isocyanatefeedstock. The foam manufacturer may then be able to obtain such mainfeedstocks already prepared for use from his suppliers, which willsimplify his manufacturing process.

It is a feature of the invention that the foam formulations givingharder and softer foam can be prepared from a main isocyanate stream anda main polyol stream. The necessary changes in hardness are thenobtained by introducing an additive when required into the mixing deviceor a stream flowing to the mixing device. Thus the polyol stream can beformulated to give a relatively hard foam with the isocyanate used, anda chain extender may be fed into the mixing device, either directly orby addition to the main polyol stream, to give a formulation givingsofter foam.

Conversely the main polyol stream may be one which gives with theisocyanate used a relatively soft foam. A cross linker may then beadded, in the same way as the chain extender mentioned above, to give aharder foam.

Similarly an isocyanate stream containing more or less polyphenylmethylene polyisocyanate may be used in addition to the main isocyanatestream to adjust the hardness of the foam.

It is desirable to control the relative reactivity of the two foamformulations used to obtain relatively hard and soft parts.

The first formulation fed to the mould is preferably less reactive thanthe second formulation fed to the mould.

Preferably the second formulation has a cream time which is at least t-1seconds (where t is the cream time in seconds of the first formulation)more preferably at least t-2 seconds.

The first formulation fed to the mould preferably has a cream time inthe range 2 to 7 seconds.

Cream time is defined as the time in seconds from the time of mixing thefoam-forming ingredients and the onset of creaming which is a colourchange from clear to milky which takes place when the liquid begins toexpand.

Cream time can be affected by the nature of the polyol and isocyanateused and by the nature and amount of catalyst used and those skilled inthe formulation of polyurethane will readily understand how to obtainsuitable cream times.

The second formulation is introduced directly on to the firstformulation (i.e. in the absence of any separating device), at a timecorresponding to a volume expansion of the first foam formulation in therange +100% to 2300%. Preferably the second foam formulation is firstintroduced at a time corresponding to a volume expansion of the firstfoam formulation in the range +250% to +1400% The second formulation ispreferably first introduced into the mould at a time between t+3 secondsand t+15 seconds (where t is the cream time of the first formulation)after the introduction of the first formulation has begun morepreferably t+3 to t+7 seconds.

The pre-polymer technique can be used in which the polyol is reactedwith an excess of polyisocyanate to give a pre-polymer which is foamedin a second step by the action of a blowing agent, usually water.Alternatively the one shot technique may be used in which reaction ofthe polyol and isocyanate and the foaming reaction take place in asingle step.

The present invention will now be further described by reference to thefollowing drawings, which are not to be deemed limitative of the presentinvention in any manner thereof.

FIG. 1 shows the addition of a first foam formulation.

FIG. 2 shows the initial foaming of the first foam formulation.

FIG. 3 shows the addition of a second foam formulation.

FIGS. 4 and 5 show the encapsulation of the second foam by the firstfoam.

FIG. 6 shows the encapsulated second foam after foaming is completed.

FIG. 1 shows the addition into the mold of a first foam formulationthrough nozzle 1, which is for adding the first foam formulation intothe mold. Also shown in FIG. 1 is nozzle 2 which is for adding a secondfoam formulation into the mold.

In FIG. 1 a measured amount of the first foam formulation 3 is added tothe bottom of the mold. This first foam formulation 3 is introduced in aliquid form. Within a very few seconds, the reaction between the polyolcomponent and the isocyanate component of the reaction mixture begins,and causes the material in the mold to expand.

The expansion of the first foam formulation will produce the first foam4, which is a soft foam, and is shown in FIG. 2. The expanding softfirst foam continues to expand, and to increase in volume, as shownprogressively by the successive increases in the volume of foam 4 inFIGS. 2, 3, 4, 5 and 6. In other words, FIG. 2 shows the initial foamingof the soft first foam formulation.

At a time corresponding to a volume expansion for the soft first foamformulation, in the range of +100% to +2300%, the addition of the secondfoam formulation 5 through nozzle 2 onto a portion of the top surface ofthe first foam 4 takes place.

FIGS. 4 and 5 show that there is an encapsulation of the second or firmfoam 6 taking place by the soft first foam 4. The second foamformulation 5 of FIG. 3 starts expanding in order to produce the hardfoam 6 which is shown in FIGS. 4, 5 and 6. THe second or firm hard foam6 is harder and firmer than the soft first formulation 4, even thoughthe second foam formulation 6 continues to expand and to progressivelyincrease in volume as shown sequentially in FIGS. 4, 5 and 6.

As can be seen from FIGS. 4, 5 and 6, the soft first foam 4 continues toexpand at such a rate that it will eventually surround and encapsulatethe second hard foam, after the foaming has been completed. Thus, FIG. 6shows the encapsulated second foam which is surrounded by, and embeddedwithin, the first soft foam, after the foaming has been completed byboth foams 4 and 6.

In summary, the second foam formulation is introduced directly on to aportion of the first formulation, at a time corresponding to a volumeexpansion of the first foam formulation in the range +100% to +2300%.The time of this volume expansion of the first foam formulation occursin at least the cream stage but before the tacky stage. The second foamformulation settles within a cavity in the first foam formulation. Thefirst foam formulation is foaming, and continues to foam, and to expandat a rate greater than the rate of foaming expansion of the secondfoaming formulation, so that the first foaming formulation flows overand around the second foaming formulation, so as to form one or morerelatively hard regions embedded within and surrounded by the relativelysoft foam.

THE POLYOL

In producing cellular urethane polymers the reaction mixture or foamformulation contains an active hydrogen-containing organic compoundhaving an average of at least two and usually not more than six activehydrogen atoms present as hydroxyl groups. Such organic polyol reactantsinclude compounds consisting of carbon, hydrogen and oxygen as well ascompounds which contain these elements in combination with phosphorus,halogen and/or nitrogen. Suitable classes of organic polyol reactantsfor use in the method of this invention are polyether polyols, polyesterpolyols, polyactone polyols, nitrogen-containing polyols,phosphorus-containing polyols, phenolic-based polyols, andpolymer/polyols produced by polymerising an ethylenically unsaturatedmonomer in one of the aforesaid polyols in the presence of a freeradical initiator, or reacting isocyanates with primary and/or secondaryamino groups containing polyaminesand/or hyrazines in presence of abovementioned polyols, as described in the German Offenlegungsschrift No. 2519 044 (4.11.76).

It is well known to the polyurethane art that the particular polyolreactant or combination of polyols employed depends upon the end-use ofthe polyurethane product.

For this purpose the polyol is usually characterised by its hydroxylnumber which is determined by and defined as the number of milligramspotassium hydroxide required for the complete neutralisation of thehydrolysis product prepared by hydrolysing an ester derived from 1 g ofpolyol or mixture of polyols. The hydroxyl number is also defined by thefollowing equation which reflects its relationship with thefunctionality and molecular weight of the polyol. ##EQU1## OH=hydroxylnumber of polyol f=average functionality, that is, average number ofhydroxyl groups per molecule of polyol

M.W=average molecular weight of the polyol.

Examples of preferred polyols are those in which at least 40 weightpercent of the total polyol content is constituted of a polyether triolhaving the following additional characteristics: (a) an average primaryhydroxyl content of at least 40 mole percent (or no more than 60 molepercent of the less reactive secondary hydroxyl groups); and (b) anaverage molecular weight of from about 2000 to about 8000. Preferably,such polyether triols for use as components of high-resilienceformulations contain from about 60 to about 90 mole percent of primaryhydroxyl groups and have an average molecular weight of from about 4000to 7000. Consistent with their trifunctionality and the aforesaidrespective ranges of molecular weights, such polyether triols havehydroxyl numbers from 84 to 21, perferably from 42 to 24. These highlyreactive polyether triols are provided by oxyalkylation of one of theaforesaid trihydric starters such as glycerol, with propylene oxide andethylene oxide. Usually, the total ethylene oxide content of thepolyether triols is between about 7 and about 20 weight percent,expressed on the basis of total alkylene oxide fed during theoxyalkylation reaction. The high primary hydroxyl content is introducedby capping of the polyoxyalkylene chains with at least a portion of thetotal ethylene oxide feed.

In providing high resilience foams, the polyether triols may be used asessentially the sole type of polyol in the formulation or they may beemployed in combination with other polyols to control the degree ofsoftness or firmness of the foam to vary the load bearing properties.

In particular the polyol used may contain finely dispersed organic orinorganic materials to provide improved load bearing properties.Examples of such polyols are those prepared by polymerisingethylenically unsaturated monomers e.g. acrylonitrile andor styrene witha polyether polyol. The polyether polyol in which the polymerisationtakes place preferably has the characteristics indicated as preferredfor polyether triols above.

The products obtained by polymerising ethylenically unsaturated monomesin polyether polyols are frequently known as polymer polyols.

THE ISOCYANATE

The polyisocyanate components employed in this invention for mixing withactive hydrogen compounds preferably are those having the generalformula:

    Q(NCO).sub.i

wherein i is an integer of two or more and Q is an organic radicalhaving the valence of i. Q can be a substituted or unsubstitutedhydrocarbon group (e.g. an alkylene or an arylene group). Q can be agroup having the formula Q'--Z--Q' where Q' is an alkylene or arylenegroup and Z is --O--, --O--Q'--, --CO--. --S--, --S--Q'--S--, or --SO₂--. Examples of such compounds include hexamethylene diisocyanate,1,8-diisocyanato-p-menthane, xylene diisocyanate, (OCNCH₂ CH₂ OCH₂)₂0,1-methyl-2.4-diisocyanatocyclohexane, phenylene diisocyanate, tolylenediisocyanates, chlorophenylene diisocyanates,diphenylmethane-4.4'-diisocyanate, naphthalene-1.5-diisocyanate,triphenylmethane-4.4',4"-triisocyanate, andisopropylbenzenealpha4-diisocyanate.

Q can also represent a polyurethane radical having a valence or i inwhich case Q(NCO)_(i) is a composition conventionally known as apre-polymer. Such pre-polymers are formed by reacting a stoichiometricexcess of a polyisocyanate as set forth hereinbefore and hereinafterwith an active hydrogen-containing component as set forth hereinafter,especially the polyhydroxyl containing materials or polyols.

Further included among the isocyanates useful in this invention are thedimers and trimers of isocyanates and diisocyanates and polymericdiisocyanates such as those having the general formula:

    [Q"(NCO).sub.i ].sub.j

in which i and j are each integers of two or more, and Q" is apolyfunctional organic radical, and/or, as additional compontents in themixtures, compounds of the general formula:

    L(NCO).sub.i

in which i is one or more and L is a monofunctional or polyfunctionalatom or radical. Examples of this type include ethylphosphonicdiisocyanate, C₂ H₅ P(O)-N(NCO)₂ ; isocyanates derived from sulfonamides(QSO₂ NCO), cyanic acid, and thiocyanic acid.

More specifically, the polyisocyanate component employed in thisinvention also include the following specific compounds as well asmixture of two or more of them; 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate, crude tolylene diisocyanate,bis(4-isocyanatophenyl)methane, polyphenylmethylene polyisocyanates thatare produced by phosgenation of aniline formaldehyde condensationproducts, dianisidine diisocyanate, toluidine diisocyanate, xylylenediisocyanate, bis(2-isocyanatoethyl)fumarate,bis(2-isocyanatoethyl)carbonate, 1,6-hexamethylene-diisocyanate,1,4-tetramethylene-diisocyanate, 1,10-decamethylene-diisocyanate,cumene-2,4-diisocyanate, 4-methoxy-1,3-phenylene-diisocyanate,4-chloro-1.3-phenylenediisocyanate, 4-bromo-1,3-phenylenediisocyanate,2-ethoxyll, 3phenylenediisocyanate, 2,4'-diisocyanatodiphenylether,5,6-dimethyl 1,3-phenylenediisocyanate, 4,4'-diisocyanatodiphenylether,bis-5,6-)2-isocyanatoethyl)(bicyclo 2.2.1)hept-2-ene,benzidenediisocyanate, 4,6-dimethyl-1,3 phenylene9.10-anthracenediisocyanate, 4,4'-diisocyanatodibenzyl,3,3-dimethyl-4.4'diisocyanatodiphenylmethane,2,6-dimethyl-4,4'diisocyanatodiphenyl, 2,4-diisocyanatostilbene,3,3'-dimethoxy-4,4'diisocyanatodiphenyl, 1,4-anthracene diisocyanate,2,5-fluorenediisocyanate, 1,8-naphthalene diisocyanate,2,6-diisocyanatobenzfuran, 2,4,6-toluene triisocyanate, and many otherorganic polyisocyanates that are known in the art, such as those thatare disclosed in an article by Siefken, Ann. 562, 75 (1949). It isparticularly preferred to use 2,4- and 2,6-toluene diisocyanate,particularly mixtures of the above isomers, and polyphenyl methylenepolyisocyanates. An increase in the relative amount of tolueneisocyanates gives softer foam and an increase in the relative amount ofisocyanate with a functionality greater than two i.e. with more than twoisocyanate groups per molecule, e.g. polyphenyl methylenepolyisocyanates gives harder foam.

BLOWING AGENTS

Water and/or readily volatile organic substances are used as blowingagents in the process according to the invention.

Generally, the blowing agent is employed in an amount from about 1 toabout 15 parts by weight per 100 parts by weight of total polyolreactant, the particular blowing agent and amount thereof depending uponthe type of foam product desired. Flexible foam formulations usuallycontain no more than about 6 pphp of water. The selection and amount ofblowing agent in any particular foam formulation is well within theskill of the cellular polyurethane art. Suitable organic blowing agentsare e.g. acetone, ethyl acetate, halogenated alkanes, such as methylenechloride, chloroform, ethylidene chloride, vinylidene chloride,monofluorotrichloromethane, chlorofluoromethane ordichlorodifluoromethane, butane, hexane, heptane or diethyl ether. Ablowing effect can also be obtained by adding compound which decomposeat temperatures above room temperature to liberate gases, e.g. azocompounds such as azoisobutyric acid nitrile which liberate nitrogen.Further examples of blowing agents and details of the use of blowingagents may be found in Kunstoff-Handbuch, Volume VII, published byVieweg and Hoechtlen, Carl-Hanser-Verlag, Munnich 1966 e.g. on pages 108and 109, 453 and 507 to 510.

CATALYSTS

Catalysts are also frequently used in the process according to theinvention. The catalysts used are knwon per se, e.g. tertiary aminessuch as triethylamine, tributylamine, N-methyl-morpholine,N-ethyl-morpholine-N-Cocomorpholine,N,N,N',N'-tetramethyl-ethylenediamine, 1,4-diaza-bicyclo-(2,2,2)-octane,N-methyl-N'-dimethyl-aminoethyl-piperazine, N,N-dimethyl benzylamine,bis-(N,N-diethylaminoethyl)-adipate, N,N-diethylbenzylamine, pentamethyldiethylenetriamine, N,N-dimethylcyclohexylamine,N,N,N',N'-dimethyl-phenylethylamine, 1.2-dimethyl imidazole and2-methyl-imidazole, triethylene diamine, bis(2-dimethylaminoethyl)ether.

The tertiary amines which contain hydrogen atoms capable of reactingwith isocyanate groups may be e.g. triethanolamine, triisopropanolamine,N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylethanolamineor their reaction products with alkylene oxides such as propylene oxideand/or ethylene oxide.

Silaamines which contain carbon-silicon bonds may also be used ascatalysts, e.g. the compounds described in German patent specificationNo. 1 229 290 such as 2,2,4-trimethyl-2-silamorpholine or1,3-diethylaminomethyltetramethyl-disiloxane.

The catalysts used may also be bases which contain nitrogen such astetraalkyl ammonium hydroxides or alkali metal hydroxides such as sodiumhydroxide, alkali metal phenolates such as sodium phenolate or alkalimetal alcoholates such as sodium ethylene. Hexahydrotriazines may alsobe used as catalysts.

Organic metal compounds may also be used as catalysts according to theinvention, especially organic tin compounds.

The organic tin compounds used are preferably tin (II) salts ofcarboxylic acids such as tin (II)-acetate, tin (II) octoate, tin(II)-ethylhexonoate and tin (II)-laurate and the dialkyl tin salts ofcarboxylic acids such as dibutyl tin diacetate, dibutyl tin dilaurate,dibutyl tin maleate or dioctyl tin diacetate.

Other examples of catalysts which may be used for the process accordingto the invention and details of their mode of action are described inKunststoff-Handbuch, Volume VII, published by Vieweg and Hoechtlen,Carl-Hanser-Verlag, Munich 1966, e.g. on page 96 and 102.

The catalysts are generally used in a quantity of between 0.002 and 10%by weight, based on the quantity of compounds which contain at least twohydrogen atoms capable of reacting with isocyanates.

ORGANOSILOXANE SURFACTANT

In producing cellular polyurethanes in accordance with the method ofthis invention, a minor amount of an organosilicone surfactant may alsobe present as an additional component of the polyurethane-formingreaction mixture. When used such surfactants are usually present inamounts up to about 5 parts by weight per 100 parts by weight of totalpolyol reactant. Suitable classes of silicone surfactants are thepolysiloxane-polyoxyalkylene block copolymers wherein the respectiveblocks are joined through silicon-to-carbon orsilicon-to-oxygen-to-carbon bonds and the respective polyoxyalkyleneblocks are bonded to different silicon atoms of the polysiloxanebackbone to form a comb-like structure. Usually, the polysiloxane blocksare trialkylsiloxy end blocked. In addition to the siloxy units to whichthe pendant polyoxyalkylene chains are bonded, the polysiloxane backboneis formed of difunctional siloxy units wherein the respective tworemaining valences of silicon are satisfied by bonds to organicradicals. Illustrative of such organic radicals are the hydrocarbylgroups having from 1 to 12 carbon atoms including alkyl, aryl, aralkyl,bicycloheptyl and halogen substituted derivatives of such groups. Thepolyoxyalkylene blocks are usually constituted of oxyethylene units,oxypropylene units or a combination of such units, and thepolyoxyalkylene chains are hydroxyl-terminated or capped with amonovalent organic group such as alkyl, aryl, aralkyl, acyl, carbamyland the like. Especially useful as stabilisers of flexiblepolyether-based polyurethane foams are the block copolymers described inU.S. Pat. No. 3,305,377 and U.S. Pat. No. Re. 27,541. The copolymers ofthe latter patent contain from 40 to 200 dimethylsiloxy units asessentially the sole type of difunctional unit, and from 15 to 50 weightpercent of the oxyalkylene content of the polyoxyalkylene blocks isconstituted of oxyethylene.

The process of the present invention is preferably applied to theproduction of high resilience foams.

Because of the high reactivity of high-resilience foam formulations, thefoams are generally self-stabilising and can be obtained without the useof stabilising agents. However, it is usually desirable to include asilicone surfactant as an additional component of such formulations inorder to minimise the tendency of the foam to settle and to control celluniformity. Particularly effective for this purpose are the relativelylow molecular weight polyoxyalkylene-polysiloxane block copolymersdescribed and claimed in U.S. Pat. No. 3,741,917. Especially suitable ascomponents of high-resilience formulations are the block copolymersdescribed therein having the formula: ##STR1## wherein x has an averagevalue of from 2 to 7; b has a value from 3 to 10; z has an average valuefrom 2 to 6; a and d each has a value from 2 to 4; and R" is amonovalent hydrocarbon radical such as alkyl, aralkyl and aryl radicals,or an acyl group

Also suitable as organosilicone components of high-resilience foamformulations are the relatively low molecular weight aralkyl-modifiedpolymethylsiloxane oils described and claimed in U.S. Pat. No.3,839,384.

The organosilicone component is usually present in high-resilienceformulations on an amount between about 0.025 and about 2 parts byweight per 100 parts by weight of total polyol.

SOFTNESS CONTROL ADDITIVES

It is possible to describe any compound having two or more activehydrogens as a cross linking agent in so far as it links two shorterpolymer chains together by reaction with isocyanate groups. However itis desirable to distinguish between these compounds which cause anincrease in the length of a polymer chain and are substantiallydifunctional and which can be described as chain-extenders and thosewhich certain more than two active hydrogen atoms which cause asignificant degree of cross-linking between different polymer chains andare true cross-linkers.

CHAIN EXTENDERS

The softness of the polyurethane foam may be increased by increasing theamount of chain-extenders. Chain extenders are difunctional correspondscontaining active hydrogen (i.e. hydrogen which will react withisocyanate groups under the conditions used in foaming) which aredifunctional. Examples of suitable compounds containing active hydrogenare compounds containing hydroxyl or amines groups.

It is preferred not to use chain-extenders which react to liberate gase.g. water as this will lead to changes in the density of the foam.Examples of suitable chain extenders are diols such as ethane diol;butane-1, 2-diol, butane-1, 3-diol, butane-1, 4-diol, hexanediol,diethylene glycol, triethylene glycol, tetraethylene glycol and higherpolyglycols preferably having molecular weights in the range 2000 to3000.

CROSS-LINKERS

The hardness of polyurethane foam may be increased by increasing theamount of cross-linkers. In this specification cross-linkers arecompounds containing more than 2 active hydrogen atoms per molecule,preferably more than 3. Examples of such cross-linkers arediethanolamine, triethanolamine,N,N,N',N'-tetrakis-(2-hydroxypropyl)ethylene diamine, andphenol/formaldehyde/aniline condensation products.

The active hydrogen content of the cross-linker or chain extender ispreferably relatively high so as to allow a significant effect onhardness to be obtained without requiring an excessive amount ofadditive. The active hydrogen content may for example correspond to ahydroxyl number as low as 50 particularly when a chain extender is used.The cross-linker or chain extender preferably has an active hydrogencontent corresponding to a hydroxyl number of at least 100, morepreferably 600 to 1500.

Where the cross linker or chain extender is fed as an additive to themain reaction streams it is preferably used at the rate of 2 to 10 partsby weight per 100 parts of polyol fed in the main polyol stream.

It is possible to use a cross-linker in the polyol formulation givingsofter foam, provided that the formulation giving harder foam containsan increased quantity of cross linker and/or contains an isocyanategiving a harder foam. Similarly it is possible to use a chain extenderin the polyol giving a harder foam if the formulation giving softer foamcontains an increased quantity of chain extender or an isocyanate givingsofter foam.

ADDITIONAL INGREDIENTS

It is also sometimes desirable to include various additives in thereaction mixture such as colouring agents, fillers, flame retardants andthe like. Suitable colouring agents are, for example carbon black,titanium dioxide, methyl blue, chromium red and the like. Suitablefillers are fatty acids including tall oil fatty acids or tall oil perse, which, if desired, may be halogenated for example, with chlorine orbromine, vermiculite, saw dust, synthetic plastics including vinylpolymers such as, polyvinyl chloride, polystyrene and the like. Suitableflame retardants are antimony oxide, tris(chloroethyl)phosphate,tricresyl phosphate, triphenyl phosphate and the like.

QUANTITIES OF INGREDIENTS

The relative amounts of polyol, isocyanate, water catalyst, surfactantetc used may vary within the ranges usual for conventional polyurethanefoams for seating. The isocyanate index used may for example be 90 to115; more particularly 100 to 112. Preferably the index used inpreparing both harder and softer foam is within the range. Theisocyanate index is the amount of isocyanate used divided by thetheoretically required stoichiometric amount of isocyanate multiped byone hundred.

Polyurethane foams may be made by so-called high resiliency (HR)processes in which any heat necessary to complete the curing reaction isprovided by the exothermic heat generated by the curing reaction itself.Seats for cars, etc. are usually made by the HR process, and the processof the present invention is particularly suitable for use in HRprocesses.

The process of the present invention is preferably used in a process inwhich the foam ingredients are fed to an open mould which issubsequently closed.

The process of the present invention may be carried out using separatemixing heads for the formulations giving harder and softer foams.Alternatively a single mixing head may be used with separate distributoroutlets for the formulations giving harder and softer foams. Thedistributor outlets may be connected by suitable valves to the singlemixing head. A preferred way of carrying out the process of the presentinvention is use a single mixing head with a single outlet which iscaused to move across the area on which foam is to be deposited, and towhich is fed a polyol stream and an isocyanate stream and the variationsin hardness are obtained by feeding a third stream containing a softnesscontrol additive in addition to the polyol and isocyanate streams.

Where defined regions of foam of one hardness surrounded by regions of adifferent hardness are required as in car seats, the mixer outlet (mixerhead) is caused to move in a defined pattern across the open mould andthe flow of the third stream of softness control additive is controlledin relation to the movement of the mixer outlet so as to deposit mixtureof the required composition in different parts of the mould. Means arepreferably provided for doing this automatically.

After the foam has been introduced into the mould it is usually closedand left to allow foaming to take place.

In the embodiment in which the hardness is adjusted by mixing anadditive stream with a polyol and an isocyanate an example of thesuitable machine is one consisting of at least three metering pumps highor low pressure, for:

(a) polyol,

(b) isocyanate, and

(c) additive,

having also a mixer which is a mechanical stirrer or impingement selfcleaning mixinghead to homogenize the three metered raw materials beforepouring into the mould.

USES

The process of the present invention is particularly useful in theproduction of the bases of seats for cars and other vehicles where acentral soft portion is required with raised portions on either sidecontaining regions of increased hardness. It may also be used to makebacks for seats with harder portions to provide support embedded insofter foam, or mattresses or upholstered furniture with harder portionsincorporated therein.

The invention will now be illustrated by reference to the followingexample.

EXAMPLE

A low pressure commercially available machine for introducingpolyurethane foam mixture into a mould was used. This machine iscommercially available under the name Admiral. In addition to meteringpumps for controlling the flow of polyol and isocyanate streams it wasprovided with an additional pump for feeding a third stream at acontrolled rate to the mixing head. Total output from the mixing headwas 12 kg/min.

The foams were prepared from the following ingredients:

1. Polyol A is a blend of 40% Polyol A-1 and 60% Polyol A-2

Poly A-1: Polyether polyol produced by addition-polymerising propyleneoxide to glycerol and then addition-polymerising ethylene oxide. Thecontent of primary hydroxyl group is 75%, and the hydroxyl number is ca.34 mg/KOH/g.

Polyol A-2: Grafted polymer polyol prepared by polymerising 20 wt% ofacrylonitrile in polyol A-1. The content of primary hydroxyl group is75%, and the hydroxyl number is ca. 28 mg/KOH/g.

2. Silicone surfactant 1 is a commercially availablepolyoxyalkylenepolysiloxane block copolymer having a MW of about 500 andhaving the formula: ##STR2## wherein x has an average value of from 2 to7; b has a value from 3 to 10; z has an average value from 2 to 6; a andd each has a value from 2 to 4; and R" is a monovalent hydrocarbonradical such as alkyl, aralkyl and aryl radicals, or an acyl group.

3. TDI 80-20 is a mixture of 80% wt 2,4 and 20% 2,6-isomers of toluenediisocyanate which has been purified by distillation.

4. Crude MDI is an unrefined mixture obtained by reacting aniline withformaldehyde and then converting the amino groups to isocyanate.

Three separate streams were fed to the mixing head at various timesduring the filling of the mould. Stream I was the main polyol stream,and stream II was the isocyanate stream. Together these gave a harderfoam. When it was desired to produce a softer foam stream III containinga chain extender, namely water was fed to the mixer.

The composition of the three streams is given in Table 1.

                  TABLE 1                                                         ______________________________________                                                            parts by weight                                                               in total formulation                                      ______________________________________                                        Stream I                                                                      Polyol A            100                                                       Water               2.4                                                       Triethylenediamine  0.35                                                      Bis(2-dimethylamino ethyl)                                                                        0.05                                                      ether                                                                         Silicone surfactant 1                                                                             0.8                                                       Stream II                                                                     weight % composition of stream                                                TDI 80-20 70                                                                  Crude MDI 30                                                                  Parts by weight of stream per                                                                     33.8                                                      100 parts of polyol A                                                         Stream III                                                                    weight % composition of stream                                                Polyol A 90%                                                                  Water 8%                                                                      Bis(2-dimethyl 2%                                                             amino ethyl)                                                                  ether                                                                         Parts by weight of stream                                                                         5.0                                                       per 100 parts of polyol A                                                     ______________________________________                                        Mould Type:                                                                   Typical automotive front seat mould made from cast aluminium                  (18,8 1 volume).                                                              Conditions                                                                    ______________________________________                                        Mould temperature      50-55° C.                                       Demould time           8 min.                                                 ______________________________________                                         (Note the mould temperature corresponds almost to that obtained by the        exothermic reaction. The mould was heated externally to 50° C. and     the temperature was then controlled by a thermostat).                    

Processing:

a. Pumps 1/2/3 for streams I/II/III were started and the material pouredinto the open mould for 3.5 sec from left to right over the inner mouldsurface.

b. When the mix started creaming (after 4 sec), pumps 1 and 2 forstreams I and II were started twice for one second to pour a strip ofharder foam mix into each side of the mould first left than right fromfront to rear.

The mould was then closed and the ready made part demoulded after 8minutes.

The cream time for the formulation obtained from streams 1, 2 and 3 was5 seconds.

The cream time for the formulation from streams 1 and 2 was 7 seconds.

The formulation (Streams I and II) giving harder foam was first fed ontothe mixture giving the softer foam when this mixture had reached avolume expansion of +300%.

Result:

The demoulded part was cut after 3 days of conditioning (50% RelativeHumidity/23° C.) and density and compression force deflection (CFD)hardness (ASTM D 3574-77) was measured.

    ______________________________________                                                       in soft part                                                                          in hard part                                           ______________________________________                                        Density, kg/m.sup.3                                                                             54         67                                               CFD/50%, Pa      6700      10600                                              ______________________________________                                    

EXAMPLES 2-6

Foam polyurethane articles were prepared from the following ingredients:

Polyol A (as used in Example 1).

Catalyst A-1 (Trade Name): bis(2-dimethylaminoethyl)ether, acommercially available amine catalyst for polyurethane production.

Catalyst A-4 (Trade Name): a commercially available amine catalyst forpolyurethane production based on 3-dimethyl-N,N-dimethylaminopropionamide.

Dabco 33LV (Trade Name): a commercial amine catalyst for polyurethanefoam production based on triethylene diamine.

Cross linker 1: Quadrol (Trade Name);N,N,N',N'-tetrakis-(2-hydroxypropyl)-ethylene diamine: a diaminecommercially available cross-linking agent.

Cross linker 2: a mixture of equal parts by weight of monoethyleneglycol and a phenol/formaldehyde/aniline condensation product.

Silicon stabiliser 1: as used in Example 1.

In these Examples the following isocyanates were used:

ISO-0: 100% TDI 80-20

ISO-1: 80% wt TDI 80-20:20% wt MDI

ISO-20: 60% wt TDI 80-20:40% wt MDI

ISO-3: 100% MDI.

EXAMPLE 2

This Example shows the production of an article having harder and softerportions using a basic polyol and isocyanate combination giving a harderfoam which is modified by the addition of a chain extender to give asofter foam.

A car seat was prepared as in Example 1. The formulations to make theharder and softer foams are given in the Table. The physical propertiesof the harder and softer foam portions were measured and are given inTable 2. In this and the subsequent Examples CT is the cream time of thefoam in seconds. T is the rise time of the foam in seconds. In thisExample the quantity of isocyanate fed when stream III, the additive,was fed to the mixer was adjusted so as to maintain the indexsubstantially constant.

                  TABLE 2                                                         ______________________________________                                                             Stream II                                                          pbw     Additive (a)      (b)                                       ______________________________________                                        Stream I                                                                      Polyol A    100       MEG      6.0    --                                      Water       2.6       1.4 BDO  --     6.0                                     Cat. A - 1  0.2                                                               Cat. A - 4  0.4                                                               Cat. Dabco 33LV                                                                           0.4                                                               Silicon surfactant 1                                                                      1.0                                                               Stream II                                                                     ISO - 1     33.3               54.0   48.1                                    Index       102                106    106                                               Hard foam        soft foam                                          CT, sec     5                  7      5                                       RT, sec     80                 60     80                                      , kg/m.sup.3                                                                              51.1               42.3   44.9                                    CFD, Pa     3978               2617   2972                                    ______________________________________                                         MEG = monoethylene glycol                                                     BDO = butane1, 4diol                                                     

The formulation (Streams I and II) giving harder foam was first fed onthe mixture giving the softer foam when this mixture had reached avolume expansion of +400%.

EXAMPLE 3

This Example shows the production of an polyurethane flexible foamarticle having softer and harder portions in which the basic polyol andisocyanate combination gives a softer foam and harder foam is obtainedby changing the isocyanate used. A car seat was prepared as in Example1.

The formulations used and the physical properties of the harder andsofter foam portions are given in Table 3.

                  TABLE 3                                                         ______________________________________                                        Stream I                                                                      Polyol A         100                                                          Water            2.6                                                          Cat. A - 1       0.2                                                          Cat. A - 4       0.4                                                          Cat. Dabco 33LV  0.6                                                          Silicon surfactant 1                                                                           1.0                                                          Stream II                                                                     ISO - 1          33.5     --                                                  ISO - 3          --       48.5                                                Index            102      102                                                                  Soft foam                                                                              hard foam                                           CT, sec          5        7                                                   RT, sec          70       70                                                  Density, kg/m.sup.3                                                                            41       50                                                  CFD, Pa          2987     8103                                                ______________________________________                                    

The formulation giving harder foam was first fed onto the mixture givingthe softer foam when the mixture giving the softer foam had reached avolume expansion of +560%.

EXAMPLE 4

This Example shows the production of flexible foam parts of differenthardness by the use of a cross-linker to give harder foam. In thisExample the cross-linker was added to a previously prepared bulk polyolblend and the foam portions of different hardness were obtained bychanging the polyol used. The formulation used and physical test resultsobtained are given in Table 4.

Note that although the polyol mixture giving harder foam is shown asbeing added to as a third stream in a three inlet mixer it could alsohave been added by switching the polyol stream in a two inlet mixer.

                  TABLE 4                                                         ______________________________________                                        Polyol A         100      100                                                 Water            3.0      3.0                                                 Cat. A - 1       0.2      0.2                                                 Cat. A - 4       0.4      0.4                                                 Cat. Dabco 33LV  0.5      0.5                                                 Silicone surfactant 1                                                                          1.0      1.0                                                 Cross-linker 2   --       8.0                                                 ISO - 1          41.9     53.9                                                Index            108      108                                                                  Soft foam                                                                              hard foam                                           CT, sec          5        5                                                   RT, sec          75       65                                                  Density, kg/m.sup.3                                                                            43.6     38.6                                                CFD, Pa          3771     5266                                                ______________________________________                                    

The formulation giving harder foam was first fed onto the mixture givingthe softer foam when the mixture giving the softer foam had reached avolume expansion of +316%.

EXAMPLE 5

This is another Example showing the production of a flexiblepolyurethane foam article by variation in the composition of theisocyanate used. A foam car seat was made as in Example 1. Thecomposition of the formulation used and the results obtained are givenin Table 5.

                  TABLE 5                                                         ______________________________________                                        Stream I                                                                      Polyol A         100                                                          Water            2.6                                                          Cat. A - 1       0.3                                                          Cat. A - 4       0.4                                                          Cat. Dabco 33LV  0.5                                                          Silicone surfactant 1                                                                          1.0                                                          DEOA             3.0                                                          Stream II                                                                     ISO - 0          43.2     28.1                                                ISO - 3          --       18.7                                                Index            106      106                                                                  soft foam                                                                              hard foam                                           CT, sec          6        5                                                   RT, sec          55       50                                                  Density, kg/m.sup.3                                                                            54.6     55                                                  CFD, Pa          4654     7578                                                ______________________________________                                         DEOA = Diethanolamine                                                    

The formulation giving harder foam was first fed onto the mixture givingthe softer foam when the mixture giving the softer foam had reached avolume expansion of 640%.

EXAMPLE 6

This shows the preparation of harder and softer polyurethane parts usinga basic polyol and isocyanate stream which gives a softer foam andadjusting the hardness by adding a third stream of activehydrogen-containing compound (in this case a cross-linker which increasehardness). A car seat was prepared as in Example 1. The foamformulations used and the physical test results obtained are given inTable 6.

                                      TABLE 6                                     __________________________________________________________________________                   Stream III                                                                                        Cross                                                     Cross linker 1                                                                          DEOA TEOA linker 2                                                  (a)  (b)  (c)  (d)  (e)                                        __________________________________________________________________________    Stream I                                                                      Polyol B  100                                                                 Water     2.6                                                                 Cross linker                                                                            --   6.0  6.0  6.0  6.0  6.0                                        Cat. A - 1                                                                              0.2                                                                 Cat. A - 4                                                                              0.4                                                                 Cat. Dabco 33LV                                                                         0.6                                                                 Silicone surfactant 1                                                                   0.1                                                                 Stream II                          6.0                                        ISO - 1   33.5 45.1 40.0 43.3 46.8 43.0                                                 soft foam                                                                          hard foam                                                      Index     102  106  106  106  106  106                                        CT, sec   5    6    5    7    6    5                                          RT, sec   70   55   80   70   40   60                                         Density, kg/m.sup.3                                                                     41   42.7 40.2 66.9 50.6 36.6                                       CFD, Pa   2987 4389 3817 5354 4215 4183                                       __________________________________________________________________________     DEOA = Diethanol amine                                                        TEOA = Triethanolamine                                                   

The formulation giving harder foam was first fed onto the mixture givingthe softer foam when the mixture giving the softer foam had reached avolume expansion of +300%.

I claim:
 1. A process for the production of a flexible polyurethane foamarticle with regions of different hardness, which process comprisesintroducing into a mould a first foam formulation and a second foamformulation, the two formulations giving foam of different hardness andprepared by mixing together a polyol stream and an isocyanate stream ina mixercharacterised in that the process comprises first introducing thefirst formulation to give a relatively soft foam and then introducingthe second formulation to give a relatively hard foam, the second foamformulation being introduced directly on to the first formulation, at atime corresponding to a volume expansion of the first foam formulationin the range +100% to +2300% so as to form one or more relatively hardregions embedded within and surrounded by the relatively soft foam. 2.The process according to claim 1 wherein the second foam formulation isintroduced at a time corresponding to a volume expansion of the firstfoam formulation in the range +250% to +1400%.
 3. The process accordingto either of claims 1 or 2 wherein the second foam formulation is firstintroduced at a time in the range t+3 to t+15 seconds (where t is thecream time of the first formulation) after the introduction of the firstfoam has begun.
 4. The process according to claim 3 wherein the secondformulation is first introduced at a time between t+3 seconds and t+7seconds after the introduction of the first formulation has begun. 5.The process according to claim 1 wherein regions of differing hardnessare obtained by a change in the content of polyphenylmethyleneisocyanate between the first and second foam formulations.
 6. Theprocess according to claim 1 wherein regions of differing hardness areobtained by a change in active hydrogen containing compounds between thefirst and second foam formulations.
 7. The process according to claim 6wherein the active hydrogen containing compound has an active hydrogencontent corresponding to a hydroxyl number of at least
 50. 8. Theprocess according to claim 7 wherein the active hydrogen contentcorresponds to a hydroxyl number of 600 to
 1500. 9. The processaccording to claim 6 wherein the quantity of active hydrogen is in therange 2 to 25 parts per 100 parts of polyol.
 10. The process accordingto claim 1 wherein the two foam formulations are produced from a polyolstream and an isocyanate stream and one of the foam formulations isproduced by adding a third stream containing an active hydrogencontaining compound.
 11. The process according to claim 10 wherein theactive hydrogen containing compound is a chain extender.
 12. The processaccording to claim 3 wherein the first foam formulation has a cream timeof 2 to 7 seconds.
 13. The process according to claim 1, wherein regionsof differing hardness are obtained by a change in the content of a chainextender between the first and second foam formulations.
 14. The processaccording to claim 1, wherein regions of differing hardness are obtainedby a change in the composition of the isocyanate between the first andsecond foam formulations.
 15. The process according to claim 1, whereinregions of differing hardness are obtained by a change in the content ofa cross-linker between the first and second foam formulations.
 16. Theprocess according to claim 1, wherein said first foam has not solidifiedbefore said second foam is added.
 17. A process for the production of aflexible polyurethane foam article with regions of different hardness,which process comprises introducing into a mould a first foamformulation and a second foam formulation, the two formulations givingfoam of different hardness and prepared by mixing together a polyolstream and an isocyanate stream in a mixer,characterised in that theprocess comprises first introducing the first formulation to give arelatively soft foam and then introducing the second formulation to givea relatively hard foam, the second foam formulation being introduceddirectly on to a portion of the first formulation, at a timecorresponding to a volume expansion of the first foam formulation in therange +100% to +2300%, said time of said volume expansion of said firstfoam formulation occurring in at least the cream stage but before thetacky stage, the second foam formulation settling within a cavity in thefirst foam formulation, the first foam formulation foaming, andcontinuing to foam, and to expand at a rate greater than the rate offoaming expansion of the second foaming formulation, so that the firstfoaming formulation flows over and around the second foamingformulation, so as to form one or more relatively hard regions embeddedwithin and surrounded by the relatively soft foam.